Area and power efficient architectures of time deinterleaver for ISDB-T receivers

ABSTRACT

A method and apparatus for de-interleaving interleaved data in a deinterleaver memory in an Orthogonal Frequency Division Multiplexing (OFDM) based Integrated Services Digital Broadcasting Terrestrial (ISDB-T) receiver. In different embodiments, the apparatus comprises of a OFDM symbol counter along with a divider or a buffer pointer RAM with circular pointer logic, a first lookup table to obtain delay buffer size and interleaving lengths for a given OFDM transmission layer, and a second lookup table to obtain buffer base address and interleaving lengths for a given OFDM transmission layer.

BACKGROUND

1. Technical Field

The embodiments herein generally relate to communication systems, and more particularly to the field of de-interleaving interleaved data in orthogonal frequency division multiplexing (OFDM) communication systems, such as integrated services digital broadcasting terrestrial (ISDB-T) systems.

2. Description of the Related Art

In various communication systems, data gets distorted by channel impairments like fading, multipath prorogations, interference, Doppler Effect, etc. In case of small errors the altered bits can be corrected easily by using error correction codes, but in case of burst errors, higher numbers of data bits are altered and the transmitted data typically cannot be recovered completely. Time interleaving is performed by spreading coded symbols in time before transmission to protect data from burst errors.

OFDM based communication systems, such as ISDB-T use time interleaving to randomize modulated symbol data in the time domain in order to ensure robustness against fading interference and channel impairments. ISDB-T is used to provide many services such as data broadcasting, high definition television (HDTV), interactive TV, mobile applications, etc. ISDB-T was designed keeping in mind a mobile reception. De-interleaving requires a large memory due to the deinterleaver delay buffer and therefore, in general, the deinterleaver designs are random access memory (RAM) based. In RAM based designs, implementation of large number of memory pointers may lead to large number of counters. Such counters are generally implemented as flip-flops leading to a larger deinterleaver area and thereby resulting in greater power consumption. Hence, it would be desirable to reduce the deinterleaver area and reduce the complexity of deinterleaver design.

SUMMARY

In view of the foregoing, an embodiment herein provides an apparatus for de-interleaving interleaved data in an OFDM based ISDB-T receiver comprising of a deinterleaver memory; a OFDM symbol counter incrementing once for each OFDM symbol, wherein a practical bit width of the OFDM symbol counter is in the range of 25 bits (less conservative) to 30 bits (more conservative); a divider for calculating intra buffer offset in the deinterleaver memory for every increment of the OFDM symbol counter; a first lookup table in the deinterleaver memory for obtaining delay buffer sizes for various carriers and interleaving lengths for a given OFDM transmission layer; and a second lookup table in the deinterleaver memory for obtaining buffer base addresses for various carriers and interleaving lengths for a given OFDM transmission layer, where the bit width of the OFDM symbol counter is selected based on uninterrupted television viewing time on a particular channel.

The divider may be embodied as a combinational divider or a sequential divider. The first and second lookup tables are preferably stored in a read-only memory (ROM). Also, the first and second lookup tables may be implemented using dynamic arithmetic calculations. Preferably, the delay buffer sizes and the buffer base addresses are obtained from the first and second lookup tables for corresponding carriers and interleaving lengths for a given OFDM transmission layer.

Another embodiment, as disclosed herein, provides an apparatus for de-interleaving interleaved data in an OFDM based ISDB-T receiver comprising of a deinterleaver memory; a buffer pointer RAM adapted to store buffer pointer values, with the buffer pointer RAM using circular pointer increment logic; a first lookup table in the deinterleaver memory for obtaining delay buffer sizes for various carriers and interleaving lengths for a given OFDM transmission layer; and a second lookup table in the deinterleaver memory for obtaining buffer base addresses for various carriers and interleaving lengths for a given OFDM transmission layer, where the buffer pointer RAM size is chosen based on practical uninterrupted television viewing time on a particular channel. The buffer pointer RAM may comprise a 95×11 RAM. Moreover, the first and second lookup tables are implemented as a ROM. Preferably, the first and second lookup tables are implemented using dynamic arithmetic calculations.

Furthermore, an embodiment herein provides a method of de-interleaving interleaved data on a deinterleaver memory component in an OFDM based ISDB-T receiver using a buffer pointer random access memory (RAM) and circular pointer logic, a first lookup table to obtain delay buffer sizes for various carriers and interleaving lengths for a given OFDM transmission layer, and a second lookup table to obtain buffer base address and interleaving lengths for a given OFDM transmission layer, the method having the steps of reading a pointer value for a corresponding carrier from the buffer pointer RAM; incrementing the above read pointer value; retrieving a buffer size value for said corresponding carrier from the first lookup table; calculating intra buffer offset for a carrier by comparing said buffer size with the incremented pointer value; retrieving a buffer base address value for corresponding carrier from the second lookup table; adding calculated intra buffer offset to the buffer base address to calculate a memory address to store carrier data bits of the corresponding carrier; and storing the carrier data bits at the calculated memory address.

The RAM buffer pointer may comprise 96 stored pointer values. Also, the divider may be any of a combinational divider and a sequential divider. Moreover, the first and second lookup tables may be implemented as a ROM. Furthermore, the first and second lookup tables may be implemented using dynamic arithmetic calculations. Preferably, the delay buffer sizes and buffer base addresses are obtained for various carriers and interleaving lengths for a given OFDM transmission layer from the first and second lookup table respectively.

Also another embodiment, as disclosed herein, provides a method of de-interleaving interleaved data in a deinterleaver memory in an OFDM based ISDB-T receiver comprising of a OFDM symbol counter, a divider, a first lookup table to obtain delay buffer size and interleaving lengths for a given OFDM transmission layer, and a second lookup table to obtain buffer base address and interleaving lengths for a given OFDM transmission layer, the method performing the steps of counting received symbols by incrementing the OFDM symbol counter, where the OFDM symbol counter comprises a bit width in the range of 25 to 30 bits; retrieving a delay buffer size value for a corresponding carrier from the first lookup table; calculating intra buffer offset by dividing the OFDM symbol counter with the delay buffer size of corresponding carrier; retrieving a buffer base address for corresponding carrier from the second lookup table; combining the intra buffer offset and the buffer base address to calculate a memory address to store corresponding carrier data bits; and storing the carrier data bits at the calculated memory address. The method may further comprise implementing the first and second lookup tables as a ROM. Moreover, the method may further comprise implementing the first and second lookup tables as dynamic arithmetic calculations.

These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein will be better understood from the following detailed description with reference to the drawings, in which:

FIG. 1 illustrates a time deinterleaver buffer structure;

FIG. 2 illustrates a schematic diagram of a modulo based pointer architecture in a time deinterleaver ISDB-T receiver according to an embodiment herein;

FIG. 3 illustrates a schematic diagram of a memory based pointer architecture in a time deinterleaver ISDB-T receiver according to an embodiment herein;

FIG. 4 is a flow diagram illustrating a method according to a first embodiment herein;

FIG. 5 is a flow diagram illustrating a method according to a second embodiment herein; and

FIG. 6 illustrates test data input and output timing for various embodiments herein.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

As mentioned, there remains a need for reducing the complexity of interleaver design and at the same time, reduce the interleaver area. The embodiments herein achieve this by providing systems and methods for dividing the current symbol count by the buffer size corresponding to the current input carrier index, where the resulting modulo-output representing the exact intra-buffer offset. It should be also noted that Mode 1 is used as an example, and the same idea described in the disclosure can be applicable to Mode 2 and Mode 3 for both the architectures described below. Referring now to the drawings, and more particularly to FIGS. 1 through 5, where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments.

An ISDB-T transmitter employs time interleaving to randomize modulated OFDM symbol data in time domain in order to ensure robustness against fading interference. A convolutional interleaving scheme is used, in which every data carrier in an OFDM symbol is fed into a delay buffer of depth: b _(i) =I×((i×5)mod 96)  Eq. (1) where i is the buffer index ranging from 0 to n_(c)−1, where n_(c) is the number of data carriers per OFDM symbol (96, 192 or 384, depending on the system mode—respectively Mode 1, Mode 2, or Mode 3), and I is the interleaving length associated with a given OFDM transmission layer, which takes one of the following values: 0, 1, 2, 4, 8 or 16.

The operation of the convolution time deinterleaver in the ISDB-T receiver is the opposite in the sense that delay buffer depths are given by: b* _(i) =I×95I×((i×5)mod 96)  Eq. (2)

There are a total of 95 distinct non-zero delay buffers sizes in the deinterleaver, regardless of the system mode, since the buffer depth pattern given by Eq. (2) will repeat every 96 buffers, and also b*₁₉=b*₁₁₅=b*₂₁₁=b*₃₀₇=0, so the 19^(th), 115^(th), 211^(th) and 307^(th) data carriers in every OFDM symbol are transferred without delay.

A time deinterleaver buffer structure is illustrated in FIG. 1, showing the first 50 buffers, with the buffer depth ranging from b*₀=95 to b*₄₉=42. As can be seen from FIG. 1, the 19^(th) data carrier of the OFDM symbol is transferred without delay.

Table 1 illustrates buffer allocation in a RAM for one segment in Mode 1. It should be also noted that Mode 1 is used as an example, and the same idea described herein can be applicable to Mode 2 and Mode 3. The table shows buffer sizes and buffer base addresses in the ascending order of buffer indices. There are a total of 95 distinct buffer sizes ranging from 1 to 95, 190, 380, 760 or 1520 for I=1, 2, 4, 8 or 16, respectively.

TABLE 1 Buffer size and Address Lookup Table BUFFER BUFFER SIZE BUFFER ADDRESS INDEX for interleaving length I = for interleaving length I = i 1 2 4 8 16 1 2 4 8 16 0 95 190 380 760 1520 0 0 0 0 0 1 90 180 360 720 1440 95 190 380 760 1520 2 85 170 340 680 1360 185 370 740 1480 2960 3 80 160 320 640 1280 270 540 1080 2160 4320 4 75 150 300 600 1200 350 700 1400 2800 5600 5 70 140 280 560 1120 425 850 1700 3400 6800 6 65 130 260 520 1040 495 990 1980 3960 7920 7 60 120 240 480 960 560 1120 2240 4480 8960 8 55 110 220 440 880 620 1240 2480 4960 9920 9 50 100 200 400 800 675 1350 2700 5400 10800 10 45 90 180 360 720 725 1450 2900 5800 11600 11 40 80 160 320 640 770 1540 3080 6160 12320 12 35 70 140 280 560 810 1620 3240 6480 12960 13 30 60 120 240 480 845 1690 3380 6760 13520 14 25 50 100 200 400 875 1750 3500 7000 14000 15 20 40 80 160 320 900 1800 3600 7200 14400 16 15 30 60 120 240 920 1840 3680 7360 14720 17 10 20 40 80 160 935 1870 3740 7480 14960 18 5 10 20 40 80 945 1890 3780 7560 15120 19 0 0 0 0 0 950 1900 3800 7600 15200 20 91 182 364 728 1456 950 1900 3800 7600 15200 21 86 172 344 688 1376 1041 2082 4164 8328 16656 22 81 162 324 648 1296 1127 2254 4508 9016 18032 23 76 152 304 608 1216 1208 2416 4832 9664 19328 24 71 142 284 568 1136 1284 2568 5136 10272 20544 25 66 132 264 528 1056 1355 2710 5420 10840 21680 26 61 122 244 488 976 1421 2842 5684 11368 22736 27 56 112 224 448 896 1482 2964 5928 11856 23712 28 51 102 204 408 816 1538 3076 6152 12304 24608 29 46 92 184 368 736 1589 3178 6356 12712 25424 30 41 82 164 328 656 1635 3270 6540 13080 26160 31 36 72 144 288 576 1676 3352 6704 13408 26816 32 31 62 124 248 496 1712 3424 6848 13696 27392 33 26 52 104 208 416 1743 3486 6972 13944 27888 34 21 42 84 168 336 1769 3538 7076 14152 28304 35 16 32 64 128 256 1790 3580 7160 14320 28640 36 11 22 44 88 176 1806 3612 7224 14448 28896 37 6 12 24 48 96 1817 3634 7268 14536 29072 38 1 2 4 8 16 1823 3646 7292 14584 29168 39 92 184 368 736 1472 1824 3648 7296 14592 29184 40 87 174 348 696 1392 1916 3832 7664 15328 30656 41 82 164 328 656 1312 2003 4006 8012 16024 32048 42 77 154 308 616 1232 2085 4170 8340 16680 33360 43 72 144 288 576 1152 2162 4324 8648 17296 34592 44 67 134 268 536 1072 2234 4468 8936 17872 35744 45 62 124 248 496 992 2301 4602 9204 18408 36816 46 57 114 228 456 912 2363 4726 9452 18904 37808 47 52 104 208 416 832 2420 4840 9680 19360 38720 48 47 94 188 376 752 2472 4944 9888 19776 39552 49 42 84 168 336 672 2519 5038 10076 20152 40304 50 37 74 148 296 592 2561 5122 10244 20488 40976 51 32 64 128 256 512 2598 5196 10392 20784 41568 52 27 54 108 216 432 2630 5260 10520 21040 42080 53 22 44 88 176 352 2657 5314 10628 21256 42512 54 17 34 68 136 272 2679 5358 10716 21432 42864 55 12 24 48 96 192 2696 5392 10784 21568 43136 56 7 14 28 56 112 2708 5416 10832 21664 43328 57 2 4 8 16 32 2715 5430 10860 21720 43440 58 93 186 372 744 1488 2717 5434 10868 21736 43472 59 88 176 352 704 1408 2810 5620 11240 22480 44960 60 83 166 332 664 1328 2898 5796 11592 23184 46368 61 78 156 312 624 1248 2981 5962 11924 23848 47696 62 73 146 292 584 1168 3059 6118 12236 24472 48944 63 68 136 272 544 1088 3132 6264 12528 25056 50112 64 63 126 252 504 1008 3200 6400 12800 25600 51200 65 58 116 232 464 928 3263 6526 13052 26104 52208 66 53 106 212 424 848 3321 6642 13284 26568 53136 67 48 96 192 384 768 3374 6748 13496 26992 53984 68 43 86 172 344 688 3422 6844 13688 27376 54752 69 38 76 152 304 608 3465 6930 13860 27720 55440 70 33 66 132 264 528 3503 7006 14012 28024 56048 71 28 56 112 224 448 3536 7072 14144 28288 56576 72 23 46 92 184 368 3564 7128 14256 28512 57024 73 18 36 72 144 288 3587 7174 14348 28696 57392 74 13 26 52 104 208 3605 7210 14420 28840 57680 75 8 16 32 64 128 3618 7236 14472 28944 57888 76 3 6 12 24 48 3626 7252 14504 29008 58016 77 94 188 376 752 1504 3629 7258 14516 29032 58064 78 89 178 356 712 1424 3723 7446 14892 29784 59568 79 84 168 336 672 1344 3812 7624 15248 30496 60992 80 79 158 316 632 1264 3896 7792 15584 31168 62336 81 74 148 296 592 1184 3975 7950 15900 31800 63600 82 69 138 276 552 1104 4049 8098 16196 32392 64784 83 64 128 256 512 1024 4118 8236 16472 32944 65888 84 59 118 236 472 944 4182 8364 16728 33456 66912 85 54 108 216 432 864 4241 8482 16964 33928 67856 86 49 98 196 392 784 4295 8590 17180 34360 68720 87 44 88 176 352 704 4344 8688 17376 34752 69504 88 39 78 156 312 624 4388 8776 17552 35104 70208 89 34 68 136 272 544 4427 8854 17708 35416 70832 90 29 58 116 232 464 4461 8922 17844 35688 71376 91 24 48 96 192 384 4490 8980 17960 35920 71840 92 19 38 76 152 304 4514 9028 18056 36112 72224 93 14 28 56 112 224 4533 9066 18132 36264 72528 94 9 18 36 72 144 4547 9094 18188 36376 72752 95 4 8 16 32 64 4556 9112 18224 36448 72896

Table 2 shows the RAM size needed for one segment in Mode 1. Each buffer entry requires the number of bits equal to the data carrier soft decision width, therefore the total amount of memory required for the time deinterleaver is the combined depth of all the buffers multiplied by the data carrier bit width. This yields a very large memory size since the total combined buffer depth for one segment in Mode 1 is 72,960 entries for I=16 (see Tables 1 and 2). If the carrier bit width is assumed to be 12 bits long, the RAM memory needed will be over 10 M bits. Many times deinterleaver architectures use 95 distinct intra-buffer offset pointers (counters) implemented as flip-flops.

TABLE 2 Total RAM Size TOTAL RAM SIZE FOR 1 SEGMENT IN MODE 1 for interleaving length I = 1 2 4 8 16 4,560 9,120 18,240 36,480 72,960

For the simplest case of interleaving length I=1 there are 95 distinct buffer sizes ranging between 1 and 95, so for the time de-interleaving operation to be continuous (uninterrupted) the OFDM symbol counter should count up to the maximum value=LCM (least common multiple) of all natural numbers between 1 and 95, and then be reset to 0 and continue. If the larger values of the interleaving length parameter are considered, the OFDM symbol counter bit width will have to be greater than 130 bits to support the value of the above LCM, which is obviously impractical for hardware implementation.

If the worst case scenario is considered, where the shortest possible OFDM symbol length is 250 microseconds (Mode 1), the OFDM symbol counter gets incremented every 250 microseconds. If we consider realistic TV watching time, after which the user will switch to another channel or turn off the receiver, a practical value of bit width for the OFDM symbol counter can be used.

Table 3 shows the performance of 1 to 33-bit OFDM symbol counter in a receiver in terms of the maximum run time before the counter overflow occurs.

TABLE 3 Maximum runtimes of OFDM symbol counter OFDM Symbol Mode 1 Mode 2 Mode 3 Counter 0.00025 0.0005 0.001 Bits s/symbol s/symbol s/symbol 1 0.001 0.001 0.002 2 0.001 0.002 0.004 3 0.002 0.004 0.008 4 0.004 0.008 0.016 5 0.008 0.016 0.032 6 0.016 0.032 0.064 7 0.032 0.064 0.128 8 0.064 0.128 0.256 9 0.128 0.256 0.512 10 0.256 0.512 1.024 11 0.512 1.024 2.048 12 1.024 2.048 4.096 13 2.048 4.096 8.192 14 4.096 8.192 16.384 15 8.192 16.384 32.768 16 16.384 32.768 65.536 17 32.768 65.536 131.072 18 65.536 131.072 262.144 19 131.072 262.144 524.288 20 262.144 524.288 1,048.576 21 524.288 1,048.576 2,097.15 22 1,048.576 2,097.152 4,194.304 23 2,097.152 4,194.304 8,388.608 0 0 0.1 24 4,194.304 8,388.608 16,777.216 0 0.1 0.2 25 8,388.608 16,777.216 33,554.432 0.1 0.2 0.4 26 16,777.216 33,554.432 67,108.864 0.2 0.4 0.8 27 33,554.432 67,108.864 134,217.728 0.4 0.8 1.6 28 67,108.864 134,217.728 268,435.456 0.8 1.6 3.1 29 134,217.72 268,435.456 536,870.912 1.6 3.1 6.2 30 268,435.46 536,870.912 1,073,741.824 3.1 6.2 12.4 31 536,870.912 1,073,741.824 2,147,483.648 6.2 12.4 24.9 32 1,073,741.824 2,147,483.648 4,294,967.296 12.4 24.9 49.7 33 2,147,483.648 4,294,967.296 8,589,934.592 seconds 24.9 49.7 99.4 days

For mode 1, the counter width of 29 bits corresponds to more than one day of TV viewing and 33 bits corresponds to about a month of TV viewing time. The OFDM symbol counter is reset to zero upon reaching the end of the current TV viewing period.

FIG. 2 shows a modulo based pointer architecture in a time deinterleaver ISDB-T receiver. The architecture is described for Mode 1 where there are 96 data carriers per OFDM symbol. However, one skilled in the art would easily realize that Mode 1 is used only as an example and is not a restriction of the various embodiments as disclosed herein. It should be also noted that Mode 1 is used as an example, and the same idea described in the disclosure can be applicable to Mode 2 and Mode 3.

There are 95 de-interleaving delay buffers and one zero delay buffer in the receiver. The architecture comprises a time deinterleaver random access memory 201 where the deinterleaver buffers are stored, a OFDM symbol counter 202, a divider 207, a first lookup table (LUT) 205 for obtaining delay buffer sizes of 95 delay buffers, a second lookup table (LUT) 206 for obtaining buffer base addresses of 95 delay buffers. In different embodiments, the lookup tables 205, 206 can be implemented as a read-only memory (ROM) or using dynamic arithmetic calculations. The OFDM symbol counter 202 increments for each OFDM symbol, with bit width of OFDM symbol counter varying from 23-33 bits, while in practical applications the bit width of said OFDM symbol counter varies from 25-30 bits. The modulo divider 207 calculates the intra buffer offset for each carrier by dividing the OFDM symbol counter 202 value with the delay buffer size of the corresponding carrier obtained from the first LUT 205. The size of the dividend is 23 to 33 bits and the divisor size is up to 11 bits. The divider may be embodied as a combinational divider or a sequential divider. The adder 208 combines the intra buffers offset and buffer base address from the second LUT 206 to calculate the memory address where the input data gets stored in the time deinterleaver RAM 201.

FIG. 3 illustrates memory based pointer architecture in a time deinterleaver ISDB-T receiver. The architecture is described for Mode 1 where there are 96 data carriers per OFDM symbol. However, one skilled in the art would easily realize that Mode 1 is used only as an example and is not a restriction of the various embodiments as disclosed herein. It should be also noted that Mode 1 is used as an example, and the same idea described in the disclosure can be applicable to Mode 2 and Mode 3. There are 95 de-interleaving delay buffers and one zero delay buffer in the receiver. The architecture comprises a time deinterleaver RAM 201, a buffer pointer RAM 302, a first LUT 205 for obtaining delay buffer sizes of 95 delay buffers, a second LUT 206 for obtaining for obtaining buffer base addresses of 95 delay buffers. The buffer pointer RAM 302 stores the 95 delay buffer pointer values. The buffer pointer works with a circular pointer logic. For each data carrier the corresponding pointer value is read from the buffer pointer RAM 302, circularly incremented using an adder 303 and written back to the buffer pointer RAM 302. Adder 307 combines the intra buffers offset and buffer base address from the second LUT 206 to calculate the memory address where the input data gets stored in the time deinterleaver RAM 201. In different embodiments, the lookup tables 205, 206 can be implemented as a ROM or using dynamic arithmetic calculations.

FIG. 4, with reference to FIGS. 1 and 2, illustrates a method for de-interleaving interleaved data using memory based pointer architecture in accordance with the first embodiment herein. The method begins at step 410, where for each data carrier the corresponding pointer value is read from the buffer pointer RAM 302 and incremented using adder 303. The incremented value is stored back in the buffer pointer RAM 302. At step 420 the delay buffer size value of the corresponding carrier is retrieved from the first LUT 205. The incremented pointer value is compared with the retrieved buffer size value using circular increment logic to calculate the intra buffer offset at step 430. Circular increment logic involves adding ‘1’ to the incremented pointer value and comparing the new pointer value with the retrieved buffer size value. If the new value exceeds the buffer size, the new pointer value is zeroed out. At step 440, the buffer base address value of the corresponding carrier is retrieved from the second LUT 206. The memory address where the input data needs to be stored is calculated by adding the intra buffer offset to the retrieved buffer base address at step 450. Finally, at step 460, the data bits get stored in the deinterleaver RAM 201.

FIG. 5, with reference to FIGS. 1 and 3, illustrates a method for de-interleaving interleaved data using modulo based pointer architecture in accordance with the second embodiment herein. The method begins at step 510, where OFDM symbol counter 202 counts each received symbol. At step 520 the delay buffer size value of the corresponding carrier is retrieved from the first LUT 205. The intra buffer offset is calculated by dividing the OFDM symbol counter with retrieved delay buffer size value at step 530 using modulo divider 207. At step 540, the buffer base address value of the corresponding carrier is retrieved from the second LUT 206. The memory address where the input data needs to be stored is calculated by adding the intra buffer offset to the retrieved buffer base address at step 550. The data bits get stored in the deinterleaver RAM 201 at step 560.

FIG. 6 illustrates the test data input timing for both the modulo based pointer architecture of FIG. 2 and the memory based pointer architecture of FIG. 3. The incoming data carriers (DIN) are two clock cycles apart. The interleaving length is equal to 8. However, one skilled in the art would easily realize that an interleaving length of 8 is used as an example and is not a restriction of the embodiments as disclosed herein. Data is written into the deinterleaver RAM 201 every two-clock cycles apart. DOUT represents the data as taken out of the deinterleaver RAM 201. If the incoming data is spaced many cycles apart, the size of modulo based architecture can be reduced by making the divider a sequential divider.

The architectures provided by the embodiments herein and illustrated in FIGS. 2 and 3 results in chip area savings compared with the conventional architectures. Using an example of 0.13 um standard cell technology, one scan flip-flop is roughly 40 um², so for conventional design the 95×11 flip-flops alone will occupy up to 40,000 um². One example of sequential divider implementation with a 25-30 bit dividend is 7,000-10,000 um², plus an OFDM symbol counter of 1000-1200 um2, so the equivalent design saves about 30,000 um². For a memory-based design, a 95×11 RAM is on average 5,000-7,000 um², plus additional adder logic plus memory built-in self-test (BIST) overhead, so the equivalent design is under 10,000 um², which also saves around 30,000 um². Hence assuming that the rest of the architecture (buffer size LUT, buffer address LUT and memory address calculation logic) is the same between existing art and the proposed architectures, chip area for the intra-buffer pointer storage and calculation requires reduction.

The techniques provided by the embodiments herein may be implemented on an integrated circuit chip (not shown) and may be used in digital video broadcast systems for handheld devices, and implemented in the baseband chip sets. The chip design is created in a graphical computer programming language, and stored in a computer storage medium (such as a disk, tape, physical hard drive, or virtual hard drive such as in a storage access network). If the designer does not fabricate chips or the photolithographic masks used to fabricate chips, the designer transmits the resulting design by physical means (e.g., by providing a copy of the storage medium storing the design) or electronically (e.g., through the Internet) to such entities, directly or indirectly. The stored design is then converted into the appropriate format (e.g., GDSII) for the fabrication of photolithographic masks, which typically include multiple copies of the chip design in question that are to be formed on a wafer. The photolithographic masks are utilized to define areas of the wafer (and/or the layers thereon) to be etched or otherwise processed.

The resulting integrated circuit chips can be distributed by the fabricator in raw wafer form (that is, as a single wafer that has multiple unpackaged chips), as a bare die, or in a packaged form. In the latter case the chip is mounted in a single chip package (such as a plastic carrier, with leads that are affixed to a motherboard or other higher level carrier) or in a multichip package (such as a ceramic carrier that has either or both surface interconnections or buried interconnections). In any case the chip is then integrated with other chips, discrete circuit elements, and/or other signal processing devices as part of either (a) an intermediate product, such as a motherboard, or (b) an end product. The end product can be any product that includes integrated circuit chips, ranging from toys and other low-end applications to advanced computer products having a display, a keyboard or other input device, and a central processor.

The embodiments herein can take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment including both hardware and software elements. The embodiments that are implemented in software include but are not limited to, firmware, resident software, microcode, etc.

Furthermore, the embodiments herein can take the form of a computer program product accessible from a computer-usable or computer-readable medium providing program code for use by or in connection with a computer or any instruction execution system. For the purposes of this description, a computer-usable or computer readable medium can be any apparatus that can comprise, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.

The medium can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or apparatus or device) or a propagation medium. Examples of a computer-readable medium include a semiconductor or solid-state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk and an optical disk. Current examples of optical disks include compact disk-read only memory (CD-ROM), compact disk-read/write (CD-R/W) and DVD.

A data processing system suitable for storing and/or executing program code will include at least one processor coupled directly or indirectly to memory elements through a system bus. The memory elements can include local memory employed during actual execution of the program code, bulk storage, and cache memories which provide temporary storage of at least some program code in order to reduce the number of times code must be retrieved from bulk storage during execution.

Input/output (I/O) devices (including but not limited to keyboards, displays, pointing devices, etc.) can be coupled to the system either directly or through intervening I/O controllers. Network adapters may also be coupled to the system to enable the data processing system to become coupled to other data processing systems or remote printers or storage devices through intervening private or public networks. Modems, cable modem and Ethernet cards are just a few of the currently available types of network adapters.

The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims. 

1. An apparatus for de-interleaving interleaved data in an Orthogonal Frequency Division Multiplexing (OFDM) based Integrated Services Digital Broadcasting Terrestrial (ISDB-T) receiver, said apparatus comprising: a deinterleaver memory; an OFDM symbol counter incrementing once for each orthogonal frequency division multiplexing-OFDM symbol, wherein a bit width of said OFDM symbol counter is in the range of 23 to 33 bits; a divider for calculating intra buffer offset in said deinterleaver memory for every increment of said OFDM symbol counter; a first lookup table in said deinterleaver memory for obtaining delay buffer sizes for various carriers and interleaving lengths for a given OFDM transmission layer; and a second lookup table in said deinterleaver memory for obtaining buffer base addresses for various carriers and interleaving lengths for a given OFDM transmission layer, wherein said bit width of said OFDM symbol counter is selected based on uninterrupted television viewing time on a particular channel.
 2. The apparatus of claim 1, wherein said divider is a combinational divider.
 3. The apparatus of claim 1, wherein said divider is a sequential divider.
 4. The apparatus of claim 1, wherein said first and second lookup tables are stored in a read-only memory (ROM).
 5. The apparatus of claim 1, wherein said first and second lookup tables are implemented using dynamic arithmetic calculations.
 6. The apparatus of claim 1, wherein said delay buffer sizes and said buffer base addresses are obtained from the first and second lookup tables for corresponding carriers and interleaving lengths for a given OFDM transmission layer.
 7. A method of deinterleaving interleaved data in a deinterleaver memory in an Orthogonal Frequency Division Multiplexing (OFDM) based Integrated Services Digital Broadcasting Terrestrial (ISDB-T) receiver comprising a OFDM symbol counter, a divider, a first lookup table to obtain delay buffer size and interleaving lengths for a given OFDM transmission layer, and a second lookup table to obtain buffer base address and interleaving lengths for a given OFDM transmission layer, said method comprising: counting received OFDM symbols by incrementing said OFDM symbol counter, wherein said OFDM symbol counter comprises a bit width in the range of 23 to 33 bits; retrieving a delay buffer size value for a corresponding carrier from said first lookup table; calculating intra buffer offset by dividing said OFDM symbol counter with said delay buffer size of corresponding carrier; retrieving a buffer base address for corresponding carrier from said second lookup table; combining said intra buffer offset and said buffer base address to calculate a memory address to store corresponding carrier data bits; and storing said carrier data bits at said calculated memory address.
 8. The method of claim 7, further comprising implementing the first and second lookup tables as a read-only memory (ROM).
 9. The method of claim 7, further comprising implementing the first and second lookup tables as dynamic arithmetic calculations. 